Canadian Farm & Food Biogas Conference
5th March 2012
Key Generator Parameters affecting
Grid Connection – for Buyers and
Sellers
Aidan Foss
ANF Energy Solutions Inc.
amfoss@ieee.org
Key Generator
Parameters
ANF Energy Solutions Inc
Biogas Conference
5th March 2012
Motivation for Presentation
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Key biogas generator parameters can
significantly affect:
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Grid Access
Withstand to Power Quality
Connection Cost
This presentation seeks to explain the reasons for
this, and raise awareness for buyers and sellers
ahead of generator selection
These parameters may have less impact in other
jurisdictions using 3-wire networks and different
technical connection requirements
Key Generator
Parameters
ANF Energy Solutions Inc
Biogas Conference
5th March 2012
ANF Energy Solutions
• DG Grid Connection Specialists
• 13 Completed biogas projects
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Terryland 1&2 (360kW), Pinehedge (100kW)
Fepro (499kW), Donnandale (498kW)
Georgian Bluffs (100kW), Lanidrac (100kW)
LaForge (600kW), ENS Poultry (138kW)
Geranik (374kW), Gardiner (250kW)
Maryland (499kW), Petrocorn (499kW)
• 9 Biogas projects in progress
• Also PV, Landfill Gas, Wind & Small Hydro
Key Generator
Parameters
ANF Energy Solutions Inc
Biogas Conference
5th March 2012
The Role of the Electrical Engineer
Farmer
Proponent
Electrical
Engineer
Rules
Process
Verification
Connection
Key Generator
Parameters
Electric
Utility
Generator
Supplier
ANF Energy Solutions Inc
Often
Out-of-Province
(European)
Biogas Conference
5th March 2012
European and Ontario Grids
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•
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European distribution grids are
predominately 3-wire
Ontario distribution grid at 27.6kV,
12.5kV, 8.3kV are 4-wire, with
extensive use of 2-wire singlephase laterals
This difference particularly impacts
feeder over-voltage risk and
imbalance
Key Generator
Parameters
ANF Energy Solutions Inc
Biogas Conference
5th March 2012
Feeder Over-voltage
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With perfect voltage quality, the three feeder
voltages are:
• Of equal magnitude
• 120 degrees apart, A-B-C
Equipment connecting to 3-wire feeders is
based on phase-phase voltage (e.g. B-C)
Equipment connecting to 4-wire feeders is
often based on the voltage between a phase
and ground (e.g. B-G)
During a short-circuit fault on a 4-wire feeder,
phase-to-ground voltages could increase to
unsafe values (e.g. 120V to 208V)
C
Neutral
B
3.0
3.0
2.0
2.0
1.0
1.0
0.0
0.0
-1.0
-1.0
-2.0
-2.0
-3.0
-3.0
Key Generator
Parameters
ANF Energy Solutions Inc
Ground
normally
A
Ground
during
fault
Biogas Conference
5th March 2012
Single-Phase Laterals
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•
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In practice, voltages and currents are
not perfectly balanced, due mainly to
imperfect load balancing across the
phases
With a single-phase lateral, all the
load is on one-phase – creates
imbalance
Single-phase laterals are deployed
extensively across the Ontario rural
distribution network
Probably the biggest source of feeder
imbalance
Key Generator
Parameters
ANF Energy Solutions Inc
Biogas Conference
5th March 2012
Imbalance
2.0
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•
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Imbalance is generally regarded as
electrical pollution – it does not
convey useful power
Three-phase generators can act as
a sink to imbalance
Imbalance currents through
transformers and alternators:
• Reduces their available capacity
(thus often oversized)
• Cause heating and other
stresses
Key Generator
Parameters
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
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Biogas Conference
5th March 2012
Types of Imbalance
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Negative sequence imbalance:
• Wrong phase order: A-C-B not A-B-C
Zero sequence imbalance:
• Causes ground and neutral currents
Single-phase loads (laterals) cause roughly similar
amounts of negative and zero sequence imbalance
Europe (3-wire)
Ontario (4-wire)
Negative Sequence
1%-2% Standard
3% Standard
Zero Sequence
None
3% Standard
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Parameters
ANF Energy Solutions Inc
Biogas Conference
5th March 2012
Negative Sequence Imbalance
V2
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•
I2 = V2 / (X2+XT) Ohm’s Law
A small voltage imbalance (V2) can give rise to
a large current imbalance (I2)
Key parameters are:
• the alternator negative sequence
impedance (X2)
• the capability of the alternator to withstand
imbalance
X2 should be checked at the design stage
Site single-phase loads also cause Negative
Sequence imbalance
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Parameters
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XT
I2
SITE
LOADS
X2
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5th March 2012
Zero Sequence Imbalance
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I0 = V0 / (X0+XT) if the generator is
effectively grounded and a Y-gnd:Y-gnd
transformer is employed
Y-gnd:Y-gnd transformers avoid high voltage
equipments and thus keep costs down
 A small voltage imbalance (V0) can give
rise to a large neutral current (3xI0)
Not an issue on 3-wire networks
Key parameters are:
• the alternator negative sequence
impedance (X0)
• the capability of the alternator to withstand
neutral current
Key Generator
Parameters
ANF Energy Solutions Inc
V0
XT
Y-gnd/Ygnd
I0
SITE
LOADS
X0
3xI0
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5th March 2012
Effective Grounding
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Effective grounding limits the rise of
phase-to-ground voltages during a
single-phase fault (e.g. 120V)
Scenario of concern:
SUBSTATION
Open
• Single-phase fault on feeder
• Substation breaker/recloser opens
before generator breaker
• Generator and feeder not effectively
grounded
•
Fault
Nominal requirement before 2008 was
for generation sites to be effectively
grounded
Closed
3.0
3.0
2.0
2.0
1.0
1.0
0.0
0.0
-1.0
-1.0
-2.0
-2.0
-3.0
-3.0
Key Generator
Parameters
Feeder
with
other
Users
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Biogas Conference
5th March 2012
Feeder Reclosers
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On 27.6kV feeders, utility reclosers
generally disconnect all three
phases for any feeder fault
On 8.3kV and 12.5kV feeders,
utility reclosers generally
disconnect only one phase for a
single-phase feeder fault
The scenario of concern only
applies to 27.6kV feeders
Requirement for effective grounding
on connections to 8.3kV and
12.5kV was dropped in Fall 2008
Key Generator
Parameters
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Biogas Conference
5th March 2012
Resistance Grounding
• On biogas generators connecting to
8.3kV and 12.5kV feeders, the generally
preferred solution is:
– Employ a Y-gnd:Y-gnd transformer in order
to avoid expensive high voltage equipments
– Ground the generator neutral through a
resistor – stops virtually all neutral current –
X0 not an issue
Y-gnd/Ygnd
SITE
LOADS
• Not applicable to 27.6kV feeders – workin-progress to ground at LV
Resistor
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Parameters
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Biogas Conference
5th March 2012
Grid Access
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On many parts of the Hydro One
network, grid access is limited by:
• Thermal constraints (transformer,
feeder)
• Fault level constraints (switchgear)
Although two alternators may have the
same kW-load output, they may have
very different fault current contribution
can impact on grid access
The initial generator fault current
depends on the subtransient reactance
(Xd”)
Key Generator
Parameters
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Biogas Conference
5th March 2012
Changing/Selecting Alternators
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Changing alternators resulting in an
increase in fault current contribution can
trigger a new CIA
Changing alternators resulting in a decrease
in fault current contributions has (to date)
only required an Equipment Clarification
Frequently a proponent wants a CIA to
secure grid access ahead of alternator
selection
But, CIA is based on a specific alternator
configuration
Application is based on the candidate
alternator with the highest fault current
contribution
Key Generator
Parameters
ANF Energy Solutions Inc
?
Biogas Conference
5th March 2012
Other Key Alternator Parameters
• Other alternator parameters are
used for Protection Studies and
impact on protection settings
• Must be correct as affect ability
to detect feeder faults
• Used by utility to provide the
signature of a remote feeder
fault
Key Generator
Parameters
ANF Energy Solutions Inc
Biogas Conference
5th March 2012
Key Parameters Summary
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Subtransient Reactance (Xd”): should be checked at the design
stage as may prevent grid access and may require a new CIA
•
Negative Sequence Reactance (X2) and Negative Sequence
Withstand : should be checked at the design stage
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Zero Sequence Reactance (X0) and Neutral Current Withstand
: should be checked at the design stage if connecting to 27.6kV
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Changes to other parameters likely to result in protection study
rework for the utility and consultant
Thank you – Any Questions?
Key Generator
Parameters
ANF Energy Solutions Inc
Biogas Conference
5th March 2012